本文建立一個三國兩廠商的經濟模型，並加入廠商報酬相依性與租稅逃漏行為以探討進口國之最適差別關稅政策，模型中兩外國廠商將產品出口至進口國並作數量（價格）競爭，進口國則對兩廠商課徵差別從量關稅。本文發現，在不考慮租稅逃漏的情況下，不論兩廠商進行數量競爭或是價格競爭，亦不論廠商間的競爭程度，進口國政府仍應對高（低）成本的出口廠商課徵較低（高）的關稅；而隨著競爭程度愈高（低）或商品替代性愈高（低），稅率差額與邊際成本差額之比值愈大（小）。然而在考慮租稅逃漏的情況下，兩國關稅的高低將取決於各國的租稅環境而定；此時，傳統上「低（高）成本，高（低）關稅」的課稅原則是否成立，將決定於出口廠商之有效邊際成本及關稅對申報比例之彈性。

This paper establishes a three country two firm model, including firms’ payoff interdependence and tax evasion. In this model, two firms export products to import country and engage in quantity (price) competition, while the import country imposes discriminatory tariffs on the imports from different countries. Under the setup, we find that the product with a lower production cost should be imposed a higher tariff, and the tariff difference becomes smaller as the degree of market competitiveness or product homogeneity increases. However, taking tax evasion into consideration, the new result is that the tariff difference depends on the tax environment factors of each firm. The real tariff rate difference lies on the effective marginal cost of export firms and the tariff elasticity of declaration ratio.

第一章 緒論 1
第二章 文獻回顧 3
第一節 最適差別關稅 3
第二節 報酬相依性 4
第三節 租稅逃漏 5
第三章 考慮報酬相依性之Cournot數量競爭模型 6
第一節 基本模型設定 6
第二節 出口國廠商產出策略 6
第三節 進口國政府最適差別關稅策略 8
第四章 考慮報酬相依性之Bertrand價格競爭模型 11
第一節 出口國廠商價格策略 11
第二節 進口國政府最適差別關稅策略 12
第五章 考慮租稅逃漏之模型 16
第一節 基本模型設定 16
第二節 出口國廠商產出及逃漏策略 16
第三節 進口國政府最適差別關稅策略 17
第六章 結論 20
參考文獻 21

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